1. Field of the Invention
This invention relates to a process for the forming and bonding of titanium structures and more particularly to an inexpensive method for the superplastic forming and diffusion bonding of titanium structures concurrently by means of low pressure and Delta-Alpha tooling, that is tooling wherein the various components are constructed of materials having different degrees of expansion when heated.
2. Description of the Prior Art
Superplasticity has been known since extraordinary elongations in metals were first observed by C. F. Pearson in England in 1934. Articles by Fields and Backofen (ASTM 1957), Lee and Backofen (AIME Transactions 1966 and 1967) and Chandlhani (Science and Technology Magazine 1968) and others, described superplastic behavior and identified about twenty materials which exhibited superplasticity, among them being two common titanium alloys (Ti-6Al-4V and Ti-5Al-2.5Sn).
Presently, the Super Plastic Forming/Diffusion Bonding (SPF/DB) process requires special facilities to perform the fabrication process.
In Hamilton et al., U.S. Pat. Nos. 3,920,175; 3,927,817 and 3,934,491, relatively large presses are used within a furnace or with heated platens to provide the pressures required for the SPF/DB process. In other methods high pressure autoclaves are employed with internal furnaces or heated tooling much like a hot isostatic press facility. In each different method, specialized facilities are required to contain the high pressure gas environment by which either the diffusion bonding or superplastic forming or both processes are performed.
Titanium is a highly reactive material at the superplastic forming and diffusion bonding temperature range, accordingly, the material must be protected from air at those temperatures. Common practice is to protect the material in an environment of inert gas, such as argon, helium or the like or by use of a vacuum.
Delta-Alpha tooling systems are well known in the prior art.
There has not been an entirely satisfactory low-cost method of simultaneously producing structures by superplastic forming/diffusing bonding until the emergence of the instant invention.